I never had this problem before, but each time I try to post an attachment, I keep getting an error message saying I am not logged in. I log back in and attempt to post, but it keeps returning me to to same error message. What can I do about this?

You probably have some corrupt cookies. Try deleting the cookies in your browser and log in again.

Good news is that I added my name and password to "Remember Me" to the prompt, and I was able to post without problems.